560SL Timing Chain Replace
 

Hi,

My 560SL has about 107k miles on it. I was wondering if someone can help me about if I should have the timing chain replace at this milleage. Should I have the rails replaced too? Also, any idea on how much it would cost?

Thanks for your help.

timing chain
 

I spoke with a MB mechanic in San Antonio last week about this and he seems convinced that the chain should be replaced at around 100K miles. But the interesting thing he said is that the sprokets don't really have to be replaced. Now, I have been doing mechanics for about 50 years and worked with a lot of chains and sprokets on all kinds of big equipment. Always the rule is that if you replace the chain you replace the sproket, without question. An old sproket will eat up a new chain in no time.

The problem is that replacing the chain is a relatively minor job. Replacing the gears and or guides becomes major real fast. To replace the guides and sprokets apparently (according to the Haynes manual) one must remove the heads. I think that this will take a DIY chain job from $200 to a dealer job of probably $2,000.

The other money sink hole is that if you have the heads off you might as well do a valve job. There is another $1,000. Will it ever end?

Some one please tell me that this isn't the case.

Two mechanics (at different shops) told me that you should check for chain tension whenever you drain the oil and use that to determine when to replace the chain. Before the chain can hop a tooth (they rarely break outright, I'm told), it must have stretched enough to have slack beyond what the tensioner can take up.

Both suggested that I not change my chain as long as it's still tight (tightness can be checked with the cam covers off).

Could be wrong, but that's what I was told.

My understanding from all I have read is that it is not just the chain you worry about. Another issue on the 560 engine seems to be that the guides become brittle and pieces will break off and jam the chain. When that happens, you are looking at several thousand dollars in repairs. Do a search in the tech section since I think this was covered fairly recently. My new '88 SL had a new chain before 100k but from the invoice (P.O. had the work done), they did NOT replace the guides, so it looks like I get to do them this spring.

How much does a double sprocket & chain change the "100,000 miles" rule? Don't the 5.6's have a double timing chain?

It doesn't. The chain guides can deteriorate and break on an M117. When this happens, the broken piece can wedge between the chains and cam gears and jump the timing.

Exactly. Talk to a Mercedes technician and he will tell you this is what will usually happen.

The chain develops more slack than the tensioner can tighten up, and the loose chains slaps against the plastic guide rails. The plastic is old and has become so brittle that finally one morning on start-up, the guide breaks and the plastic pieces bind up between the chain and sprocket.

The only debate I usually hear over this subject is whether one should replace just the upper guides or both the upper and lower guides. The upper guides aren't that hard to replace, but to replace the lower guides is a LOT of labor. I had all of my guide rails and the chain tensioner replaced about a year and a half ago. The previous owner had replaced the chain, but not the guide rails. I had my car in getting new valve cover seals and they noticed that one of the upper rails was broken. I had them go ahead and replace all of the rails. Cost me just over $700, but that was without a new chain (which aren't that much anyway). My car had about 97k miles at the time.

There's something to be said about having peace of mind knowing that the single largest cause of catastrophic failure for your engine has just been taken care of. I'd recommend replacing the chain, tensioner and both upper and lower guide rails every 100k miles.

Is this merely mileage dependent or is time a factor. I am reading in this post that parts get brittle -- as you all know they get brittle over time. too. So, is a 17 year old car with about 50k miles due for a new chain?

If the double timing chain didn't make it any more durable, why did they start doing it?

Yes, a dual chain is usually more durable than a single chain, but a timing chain, whether single or double row, can still be displaced by a piece of a broken guide rail. If you are going through the trouble to replace the guide rails as a preventative maintenance measure, might as well also replace the chain and tensioner at that time.

Your mechanic can check the degrees of stretch of the chain (5 degrees being the limit, I think), but I know that I would at minimum change the upper guide rails. Seventeen year old plastic has to be as brittle as a saltine cracker.

God bless our wives for puting up with us.

Amen to that, brother, but I have to say I'm on a much shorter leash than I used to be.

My Mercedes wasn't as "bullet-proof" as it was supposed to be, what with several thousand dollars of repairs in two years: engine wiring harness, throttle actuator, complete head job, etc.

If it wasn't for my charming nature, I would have lost some credibility...:D :eek:

The chain tensioner can me a major cause
 

When I replaced my timing rails I took care to measure how much of the 12 degree 'stretch' was from various components. Replacing the chain tensioner made the most difference - 3 degrees of the 12. The new upper rails/tensioner rail took out another 2 each side, so I was down to 5 degrees of true chain stretch. I opted to leave the chain in place (it is 100,000 miles old) until it stretched to 7-8 degrees (MB sells offset Woodsruff keys to compensate for up to 10 degrees of stretch, which suggests they can live with 12 degrees). The ignition timing in the 560 is electronic and adjusts for this (the earlier 116 engine - e.g. 380 - has manual timing adjusted by twisting the ignition distributor on its axis You do not need to remove the engine cover to do this job.

Much expert comment from various mechanics suggests a life of 350,000 miles for the lower rails - where you do have to remove the engine cover for replacement.

I documented the job and you can see how dramatically the plastic rails change color with age. I do not know if that is bad as I have not done before-after brittleness tests, but I constantly read they get brittle, a piece breaks, rides up the sprocket and forces the chain to jump a tooth, with expensive consequences.

You can change the tensioner without removing anything from the engine (use 50mm M8 bolts to start it in place - new ones are very tough to push in towards the block to get the shorter factory bolts started) but you do have to remove at least one cam cover to measure stretch - the method is illustrated on my site.

If you DIY, cost is modest - $100 for the tensioner and rails, etc and another $60 or so for the chain. Just running through a new chain is easy, but not necessarily the answer - the labor is in the rails. It took me three casual afternoons to do - much messing about with the dog during the process to keep my morale high when I got stuck!